Photoelectric conversion element and imaging device

ABSTRACT

A photoelectric conversion element according to an embodiment of the present disclosure includes: a first electrode including a plurality of electrodes independent from each other; a second electrode disposed to be opposed to the first electrode; an n-type photoelectric conversion layer including a semiconductor nanoparticle, the n-type photoelectric conversion layer being provided between the first electrode and the second electrode; and a semiconductor layer including an oxide semiconductor material, the semiconductor layer being provided between the first electrode and the n-type photoelectric conversion layer.

TECHNICAL FIELD

The present disclosure relates, for example, to a photoelectricconversion element having a photoelectric conversion layer including asemiconductor nanoparticle, and an imaging device including thephotoelectric conversion element.

BACKGROUND ART

The pixel size of imaging devices such as CCD (Charge Coupled Device)image sensors or CMOS (Complementary Metal Oxide Semiconductor) imagesensors has been decreasing. An imaging device including a photoelectricconversion section outside a semiconductor substrate generallyaccumulates charges generated by photoelectric conversion in a floatingdiffusion layer (floating diffusion; FD) formed inside the semiconductorsubstrate.

Incidentally, an imaging device provided with a photoelectric conversionsection inside a semiconductor substrate temporarily accumulates chargesgenerated by photoelectric conversion in the photoelectric conversionsection inside the semiconductor substrate, and then transfers thecharges to FD. This makes it possible to completely deplete aphotoelectric conversion section. In contrast, the charges generated bya photoelectric conversion section provided outside a semiconductorsubstrate are directly accumulated in FD as described above, and it isthus difficult to completely deplete the photoelectric conversionsection. This increases kTC noise and leads to more unfavorable randomnoise, bringing about imaging quality degradation.

To address this, for example, PTL 1 discloses an imaging elementprovided with an electrode for charge accumulation. The electrode forcharge accumulation is disposed on a first electrode side of the firstelectrode and a second electrode to be spaced apart from the firstelectrode and opposed to a photoelectric conversion layer with aninsulation layer interposed therebetween. The first electrode and thesecond electrode are disposed to be opposed to each other with thephotoelectric conversion layer interposed therebetween. The firstelectrode is disposed on the opposite side to a light incidence side.This imaging element is able to accumulate charges generated byphotoelectric conversion in the photoelectric conversion layer, and itis possible to completely deplete the charge accumulation section whenexposure is started. Accordingly, it is possible to reduce imagingquality degradation.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No.2017-157816

PTL 2: Japanese Unexamined Patent Application Publication No.2010-177392

SUMMARY OF THE INVENTION

Incidentally, for example, PTL 2 discloses a photoelectric conversionelement in which a semiconductor nanoparticle is used for aphotoelectric conversion layer as a recently developed photoelectricconversion element having a sensitivity to near-infrared light. Thephotoelectric conversion element having a photoelectric conversion layerformed therein by using a semiconductor nanoparticle is required toincrease quantum efficiency.

It is desirable to provide a photoelectric conversion element and animaging device that make it possible to increase the quantum efficiency.

A photoelectric conversion element according to an embodiment of thepresent disclosure includes: a first electrode including a plurality ofelectrodes independent from each other; a second electrode disposed tobe opposed to the first electrode; an n-type photoelectric conversionlayer including a semiconductor nanoparticle, the n-type photoelectricconversion layer being provided between the first electrode and thesecond electrode; and a semiconductor layer including an oxidesemiconductor material, the semiconductor layer being provided betweenthe first electrode and the n-type photoelectric conversion layer.

An imaging device according to an embodiment of the present disclosureincludes a plurality of pixels each provided with one or morephotoelectric conversion elements, and includes the photoelectricconversion element according to the above-described embodiment as thephotoelectric conversion element.

In the photoelectric conversion element and the imaging device accordingto the respective embodiments of the present disclosure, the n-typephotoelectric conversion layer including the semiconductor nanoparticleis provided as a photoelectric conversion layer on the semiconductorlayer provided between the first electrode and the second electrodedisposed to be opposed to each other. This suppresses chargerecombination, the charges having been generated by photoelectricconversion by applying a strong electric field to the n-typephotoelectric conversion layer.

According to the electric conversion element and the imaging device ofthe respective embodiments of the present disclosure, the n-typephotoelectric conversion layer including the semiconductor nanoparticleis provided as the photoelectric conversion layer, which makes itpossible to apply a strong electric field to the n-type photoelectricconversion layer stacked on the semiconductor layer. Therefore, itbecomes possible to suppress the charge recombination in thephotoelectric conversion layer, and to increase the quantum efficiency.

It is to be noted that the effects described above are not necessarilylimitative. With or in the place of the above effects, there may beachieved any one of the effects described in this specification or othereffects that may be grasped from this specification.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view of an imaging elementaccording to an embodiment of the present disclosure.

FIG. 2 is a schematic cross-sectional view of a photoelectric conversionelement illustrated in FIG. 1.

FIG. 3 is an equivalent circuit diagram of the imaging elementillustrated in FIG. 1.

FIG. 4 is a schematic diagram illustrating disposition of a lowerelectrode and a transistor included in a control section of the imagingelement illustrated in FIG. 1.

FIG. 5A is a diagram describing an operation principle of aphotoelectric conversion element illustrated in FIG. 1.

FIG. 5B is a diagram describing an operation principle of aphotoelectric conversion element illustrated in FIG. 1.

FIG. 5C is a diagram describing an operation principle of aphotoelectric conversion element illustrated in FIG. 1.

FIG. 6A is a schematic cross-sectional view for describing a method ofmanufacturing the imaging element illustrated in FIG. 1.

FIG. 6B is a schematic cross-sectional view illustrating a stepsubsequent to FIG. 6A.

FIG. 6C is a schematic cross-sectional view illustrating a stepsubsequent to FIG. 6B.

FIG. 6D is a schematic cross-sectional view illustrating a stepsubsequent to FIG. 6C.

FIG. 6E is a schematic cross-sectional view illustrating a stepsubsequent to FIG. 6D.

FIG. 7 is a timing chart illustrating an operation example of aphotoelectric conversion element illustrated in FIG. 1.

FIG. 8 is a diagram of potential distribution between electrodes when aphotoelectric conversion element serving as a comparative example isirradiated with light.

FIG. 9 is a diagram of potential distribution between electrodes whenthe photoelectric conversion element illustrated in FIG. 1 is irradiatedwith light.

FIG. 10 is a block diagram illustrating a configuration of an imagingdevice including the imaging element illustrated in FIG. 1 as a pixel.

FIG. 11 is a functional block diagram illustrating an example of anelectronic apparatus (camera) including the imaging device illustratedin FIG. 10.

FIG. 12 is a block diagram depicting an example of a schematicconfiguration of an in-vivo information acquisition system.

FIG. 13 is a view depicting an example of a schematic configuration ofan endoscopic surgery system.

FIG. 14 is a block diagram depicting an example of a functionalconfiguration of a camera head and a camera control unit (CCU).

FIG. 15 is a block diagram depicting an example of schematicconfiguration of a vehicle control system.

FIG. 16 is a diagram of assistance in explaining an example ofinstallation positions of an outside-vehicle information detectingsection and an imaging section.

FIG. 17 is a characteristic diagram illustrating a relationship betweena doping concentration and quantum efficiency of a photoelectricconversion layer according to a working example.

MODES FOR CARRYING OUT THE INVENTION

In the following, some embodiments of the present disclosure aredescribed in detail with reference to the drawings. It is to be notedthat description is given in the following order.

-   -   1. Embodiment (example of photoelectric conversion element        provided with n-type photoelectric conversion layer)    -   1-1. Configuration of Imaging Element    -   1-2. Method of Manufacturing Imaging Element    -   1-3. Method of Controlling Imaging Element    -   1-4. Workings and Effects    -   2. Application Examples    -   3. Working Examples

FIG. 1 schematically illustrates the cross-sectional configuration of animaging element (imaging element 1) according to an embodiment of thepresent disclosure. FIG. 2 is a schematic enlarged view of thecross-sectional configuration of a main part (photoelectric conversionelement 10) of the imaging element 1 illustrated in FIG. 1. FIG. 3 is anequivalent circuit diagram of the imaging element 1 illustrated inFIG. 1. FIG. 4 schematically illustrates the disposition of a lowerelectrode 11 and a transistor included in a control section of theimaging element 1 illustrated in FIG. 1. This imaging element 1 isincluded in one pixel (unit pixel P), for example, in an imaging device(imaging device 100; see FIG. 10) such as a CMOS image sensor.

(1-1. Configuration of Imaging Element)

The imaging element 1 is provided, for example, with the photoelectricconversion element 10 on a first surface (back surface) 30A side of asemiconductor substrate 30. The photoelectric conversion element 10according to the present embodiment includes an n-type dopedphotoelectric conversion layer (n-type photoelectric conversion layer14) including a semiconductor nanoparticle between the lower electrode11 (first electrode) and an upper electrode 15 (second electrode)disposed to be opposed to each other. A semiconductor layer 13 isprovided between the lower electrode 11 and the n-type photoelectricconversion layer 14 with an insulation layer 12 interposed therebetween.The lower electrode 11 includes a readout electrode 11A, an accumulationelectrode 11B, and a transfer electrode 11C as a plurality of electrodesindependent from each other. The transfer electrode 11C is disposed, forexample, between the readout electrode 11A and the accumulationelectrode 11B. The accumulation electrode 11B and the transfer electrode11C is covered with the insulation layer 12. The readout electrode 11Ais electrically coupled to the semiconductor layer 13 via an opening 12Hprovided to the insulation layer 12.

It is to be noted that, in the present embodiment, a case is describedwhere the electron of a pair of an electron and a hole (electron-holepair) generated by photoelectric conversion is read out as a signalcharge. In addition, in the drawings, “+ (plus)” attached to “p” or “n”indicates that the concentration of p-type or n-type impurities is high,and “++” indicates that the concentration of p-type or n-type impuritiesis further higher than “+”.

The photoelectric conversion element 10 is a photoelectric conversionelement that absorbs the light corresponding to a portion or the wholeof a selective wavelength range (e.g., 700 nm or more and 2500 nm orless) to generate an electron-hole pair. The photoelectric conversionelement 10 has a configuration in which the lower electrode 11, theinsulation layer 12, the semiconductor layer 13, the n-typephotoelectric conversion layer 14, and the upper electrode 15 arestacked in this order, for example, on the first surface 30A side of thesemiconductor substrate 30 as illustrated in FIG. 2. It is to be notedthat FIG. 2 omits a fixed charge layer 16A, a dielectric layer 16B, aninter-layer insulation layer 17, and the like. The lower electrode 11is, for example, separately formed for each unit pixel P. The lowerelectrode 11 also includes the readout electrode 11A, the accumulationelectrode 11B, and the transfer electrode 11C that are separated fromeach other by the insulation layer 12 as described in detail below. FIG.1 illustrates an example in which the semiconductor layer 13, the n-typephotoelectric conversion layer 14, and the upper electrode 15 areseparately formed for each imaging element 1. However, the semiconductorlayer 13, the n-type photoelectric conversion layer 14, and the upperelectrode 15 may be provided, for example, as a continuous layer commonto the plurality of imaging elements 1.

As described above, the lower electrode 11 includes, for example, thereadout electrode 11A, the accumulation electrode 11B, and the transferelectrode 11C that are independent from each other. For example, it ispossible to form the lower electrode 11 by using anelectrically-conductive material (transparent electrically-conductivematerial) having light transmissivity. For example, the transparentelectrically-conductive material preferably has a band gap energy of 2.5eV or higher, and desirably has a band gap energy of 3.1 eV or higher.The transparent electrically-conductive material includes a metallicoxide. Specific examples thereof include indium oxide, an indium tinoxide (ITO: Indium Tin Oxide including Sn-doped In₂O₃, crystalline ITO,and amorphous ITO), an indium zinc oxide (IZO: Indium Zinc Oxide)obtained by adding indium as a dopant to zinc oxide, an indium galliumoxide (IGO) obtained by adding indium as a dopant to gallium oxide, anindium gallium zinc oxide (IGZO: In—GaZnO₄) obtained by adding indiumand gallium as dopants to zinc oxide, an indium tin zinc oxide (ITZO)obtained by adding indium and Tin as dopants to zinc oxide, IFO (F-dopedIn₂O₃), tin oxide (SnO₂), ATO (Sb-doped SnO₂), FTO (F-doped SnO₂), zincoxide (including ZnO doped with another element), an aluminum zinc oxide(AZO) obtained by adding aluminum as a dopant to zinc oxide, a galliumzinc oxide (GZO) obtained by adding gallium as a dopant to zinc oxide,titanium oxide (TiO₂), a niobium titanium oxide (TNO) obtained by addingniobium as a dopant to titanium oxide, antimony oxide, a spinel oxide,and an oxide having a YbFe₂O₄ structure. Additionally, a transparentelectrode including a gallium oxide, a titanium oxide, a niobium oxide,a nickel oxide, or the like as a base layer may be exemplified. The filmthickness (that is referred to simply as thickness below) of the lowerelectrode 11 in the Y-axis direction is, for example, 2×10⁻⁸ m or moreand 2×10⁻⁷ m or less, and preferably 3×10⁻⁸ m or more and 1×10⁻⁷ m orless.

It is to be noted that, in a case where the transparency is not requiredin the lower electrode 11, for example, it is possible to form the lowerelectrode 11 as a single-layer film or a stacked film using a metal suchas platinum (Pt), gold (Au), palladium (Pd), chromium (Cr), nickel (Ni),aluminum (Al), silver (Ag), tantalum (Ta), tungsten (W), copper (Cu),titanium (Ti), indium (In), tin (Sn), iron (Fe), cobalt (Co), ormolybdenum (Mo), or an alloy thereof. Specifically, the lower electrode11 may be formed using Al—Nd (an alloy of aluminum and neodymium), ASC(an alloy of aluminum, samarium, and copper), or the like. Further, itis possible to form the lower electrode 11 by using anelectrically-conductive material such as a conductive particle includingthe above-mentioned metal or the alloy thereof, polysilicon containingimpurities, a carbon-based material, an oxide semiconductor material, acarbon nanotube, or graphene. In addition, the lower electrode 11 may beformed by using an organic material (conductive polymer) such aspoly(3,4-ethylenedioxythiophene)/polystyrenesulfonic acid [PEDOT/PSS],and may be formed by mixing these electrically-conductive materials intoa binder (polymer) to form a paste or an ink, and curing the paste orthe ink.

The readout electrode 11A transfers the signal charges generated in then-type photoelectric conversion layer 14 to a floating diffusion FD1.The readout electrode 11A is coupled to the floating diffusion FD1provided on a second surface (front surface) 30B side of a semiconductorsubstrate 20, for example, via an upper first contact 17A, a pad section39A, a through electrode 34, a coupling section 41A, and a lower secondcontact 46.

The accumulation electrode 11B accumulates, in the semiconductor layer13, the signal charges (electrons) of the charges generated in then-type photoelectric conversion layer 14. It is desirable that theaccumulation electrode 11B be larger than the readout electrode 11A,allowing the accumulation electrode 11B to accumulate many charges.

The transfer electrode 11C increases the efficiency of transferring thecharges accumulated on the accumulation electrode 11B to the readoutelectrode 11A, and is provided between the readout electrode 11A and theaccumulation electrode 11B. This transfer electrode 11C is coupled to apixel drive circuit, for example, via an upper third contact 17C and apad section 39C. The pixel drive circuit is included in a drive circuit.It is possible to independently apply respective voltages to the readoutelectrode 11A, the accumulation electrode 11B, and the transferelectrode 11C.

The insulation layer 12 electrically separates the semiconductor layer13 from the accumulation electrode 11B and the transfer electrode 11C.The insulation layer 12 is provided, for example, on the inter-layerinsulation layer 17 to cover the lower electrode 11. In addition, theinsulation layer 12 is provided with the opening 12H on the readoutelectrode 11A of the lower electrode 11. The readout electrode 11A andthe semiconductor layer 13 are electrically coupled via this opening12H. It is preferable to incline the side surface of the opening 12H tospread the side surface of the opening 12H toward the light incidenceside S1, for example, as illustrated in FIG. 2. This facilitates chargesto move from the semiconductor layer 13 to the readout electrode 11A.

Materials of the insulation layer 12 include inorganic insulationmaterials such as metallic oxide high-dielectric constant insulationmaterials including a silicon oxide-based material, silicon nitride(SiN_(x)), aluminum oxide (Al₂O₃), and the like. Examples of materialsof the insulation layer 12 may additionally include polymethylmethacrylate (PMMA), polyvinyl phenol (PVP), polyvinyl alcohol (PVA),polyimide, polycarbonate (PC), polyethylene terephthalate (PET),polystyrene, a silanol derivative (silane coupling agent) such as N-2(aminoethyl) 3-aminopropyltrimethoxysilane (AEAPTMS), 3-mercaptopropyltrimethoxysilane (MPTMS), or octadecyltrichlorosilane (OTS), novolaktype phenolic resin, a fluorine-based resin, and organic insulationmaterials (organic polymers) exemplified as a straight-chain hydrocarbonhaving, in one end thereof, a functional group that is able to be boundto a control electrode such as octadecanethiol or dodecyl isocyanate,and a combination thereof may be used. It is to be noted that examplesof a silicon oxide-based material include silicon oxide (SiO_(x)), BPSG,PSG, BSG, AsSG, PbSG, silicon oxynitride (SiON), SOG (spin-on-glass),and a low-dielectric constant material (e.g., polyaryl ether, cycloperfluorocarbon polymer and benzocyclobutene, cyclic fluorine resin,polytetrafluoroethylene, aryl ether fluoride, polyimide fluoride,amorphous carbon, and organic SOG).

The semiconductor layer 13 accumulates the signal charges generated inthe n-type photoelectric conversion layer 14, and transfers the signalcharges to the readout electrode 11A. The semiconductor layer 13preferably has a carrier density of 10¹⁴ cm⁻³ or more and 10¹⁷ cm⁻³ orless, for example. The semiconductor layer 13 is preferably formed byusing a material having a higher charge mobility than that of the n-typephotoelectric conversion layer 14 and having a large band gap. Thismakes it possible, for example, to transfer charges at higher speed andsuppress hole injection from the readout electrode to the semiconductorlayer.

The semiconductor layer 13 includes, for example, an oxide semiconductormaterial. Examples of the oxide semiconductor material include IGZO(In—Ga—Zn—O-based oxide semiconductor), ZTO (Zn—Sn—O-based oxidesemiconductor; Zn₂SnO₄), IGZTO (In—Ga—Zn—Sn—O-based oxide semiconductor;InGaZnSnO), GTO (Ga—Sn—O-based oxide semiconductor; Ga₂O₃:SnO₂), and IGO(In—Ga—O-based oxide semiconductor). It is preferable to use at leastone of the above-described oxide semiconductor materials for thesemiconductor layer 13, and especially IGZO is favorable use. Thesemiconductor layer 13 has a thickness of 30 nm or more and 200 nm orless, for example, and preferably has a thickness of 60 nm or more and150 nm or less.

The n-type photoelectric conversion layer 14 converts light energy toelectric energy. For example, the n-type photoelectric conversion layer14 provides a field to separate, into an electron and a hole, an excitongenerated when absorbing the light within a wavelength range of 700 nmor more and 2500 nm or less. The n-type photoelectric conversion layer14 includes a semiconductor nanoparticle, and has a configuration inwhich a plurality of semiconductor nanoparticles is dispersed in anelectrically-conductive polymer, for example. A semiconductornanoparticle is a particle generally having a particle diameter ofseveral nm to several tens nm, and includes, for example, a core, ashell provided around the core, and a ligand bound to the surface of theshell. It is to be noted that the shell layer is not an essentialelement, and the semiconductor nanoparticle may include a core and aligand bound to the surface of the core. The n-type photoelectricconversion layer 14 according to the present embodiment is n-type dopedas described above. The n-type photoelectric conversion layer 14preferably has a carrier density of n=3×10¹⁶ cm⁻³ or more and 1×10¹⁸cm⁻³ or less, for example, and more preferably has a carrier density of1×10¹⁷ cm⁻³ or more and 7×10¹⁷ cm⁻³ or less.

The semiconductor nanoparticle included in the n-type photoelectricconversion layer 14 includes the following materials, for example.Examples of materials included in the core include: silicon, which is agroup IV semiconductor, and selenium; and compound semiconductors suchas chalcopyrite-based compounds including CuInGaSe, CuInSe₂, CuInS₂,CuAlS₂, CuAlSe₂, CuGaS₂, CuGaSe₂, CuZnSnSSe, ZnCuInSe, AgAlS₂, AgAlSe₂,AgInS₂, and AgInSe₂, III-V group compounds including GaAs, InAs, InP,AlGaAs, InGaP, and AlGaInP, II-VI group compounds including CdS, CdSe,CdTe, ZnO, ZnS, ZnSe, ZnTe, and HgTe, and IV-VI group compoundsincluding PbO, PbS, PbSe, and PbTe. Examples of materials included inthe shell include PbO, PbO₂, Pb₃O₄, ZnS, ZnSe, and ZnTe.

The semiconductor nanoparticle increases in band gap due toquantum-confinement effects when the particle diameter is less thantwice an exciton Bohr radius of the material. An average particlediameter of the semiconductor nanoparticle included in the n-typephotoelectric conversion layer 14 of the present embodiment ispreferably 3 nm or more and 6 nm or less, for example. Here, it isassumed that the particle diameter of the semiconductor nanoparticle isthe particle diameter of a core or the particle diameter of a coreincluding a shell in a case where the core is covered with the shell. Itis possible to adjust the size of a core and the size of a coreincluding a shell in accordance with the amount of raw materials to besupplied and a reaction condition for the synthesis thereof. The ligandincludes, for example, an absorption group that interacts with thesurface of a core or a shell, and an alkyl chain that is bound thereto.The alkyl chain includes, for example, 2 to 50 carbon atoms, andexamples of the absorption group include an amine group, a phosphonegroup, a phosphine group, a carboxyl group, a hydroxyl group, and athiol group. Additionally, halogen atoms may be used such as chlorine(Cl), bromine (Br), and iodine (I).

It is possible to change the polarity of the n-type photoelectricconversion layer 14 including the semiconductor nanoparticle, forexample, by selecting an appropriate material as a ligand included inthe semiconductor nanoparticle. Further, it is possible to change thepolarity of the n-type photoelectric conversion layer 14 including thesemiconductor nanoparticle by changing an element ratio of a coreincluded in the semiconductor nanoparticle. In the present embodiment,it is preferable that the semiconductor nanoparticle included in then-type photoelectric conversion layer 14 include PbS as a core, PbO as ashell, and halogen atoms such as chlorine (Cl), bromine (Br), and iodine(I) as a ligand, for example. In addition, in the n-type photoelectricconversion layer 14, it is preferable that the element ratio of thesemiconductor nanoparticle included in the semiconductor nanoparticle beadjusted so as to be rich in Pb. This makes it possible to make thepolarity of the n-type photoelectric conversion layer 14 to be n-type.

The n-type photoelectric conversion layer 14 has a thickness of 100 nmor more and 1000 nm or less, for example, and preferably has a thicknessof 300 nm or more and 800 nm or less.

The upper electrode 16 includes an electrically-conductive materialhaving light transmissivity. The upper electrode 16 may be separated foreach unit pixel P or formed as an electrode common to the respectiveunit pixels P. The upper electrode 16 has a thickness of 10 nm to 200nm, for example.

It is to be noted that other layers may be provided between the n-typephotoelectric conversion layer 14 and the upper electrode 15. Forexample, in a case where an electron is read out as a signal charge asin the present embodiment, a layer including a material such as MoO₃,WO₃, or V₂O₅ having a large work function may be added between then-type photoelectric conversion layer 14 and the upper electrode 15.This makes it possible to strengthen the internal electric fieldgenerated between the lower electrode 11 and the upper electrode 15.

In the photoelectric conversion element 10 according to the presentembodiment, near-infrared light L inputted to the photoelectricconversion element 10 from the upper electrode 15 side is absorbed bythe n-type photoelectric conversion layer 14. An exciton generated bythis is separated, for example, as illustrated in FIG. 5A, anddissociated into an electron and a hole. The respective charges(electrons and holes) generated here are transported to differentelectrodes, for example, as illustrated in FIG. 5B by diffusion due to adifference in carrier concentration or by an internal electric field dueto a difference in work functions between an anode (upper electrode 15here) and a cathode (lower electrode 11 here). The directions in whichan electron and a hole are transported are controlled by applying apotential between the lower electrode 11 and the upper electrode 15.Here, electrons are carried onto the lower electrode 11 side as signalcharges. The electrons carried onto the lower electrode 11 side areaccumulated in the semiconductor layer 13 above the accumulationelectrode 11B, and then transferred toward the readout electrode 11A asillustrated in FIG. 5C. The transferred electrons are detected as aphotocurrent.

The second surface 30B of the semiconductor substrate 30 is provided,for example, with the floating diffusion (floating diffusion layer) FD1(region 36B in the semiconductor substrate 30), an amplifier transistor(modulation element) AMP, a reset transistor RST, a selection transistorSEL, and a multilayer wiring line 40. The multilayer wiring line 40 hasa configuration in which wiring layers 41, 42, and 43, for example, arestacked in an insulation layer 44.

It is to be noted that the diagram illustrates the first surface 30Aside of the semiconductor substrate 30 as a light incidence side S1, andthe second surface 30B side thereof as a wiring layer side S2.

For example, the layer 16A having fixed charges (fixed charge layer),the dielectric layer 16B having insulation properties, and theinter-layer insulation layer 17 are provided between the first surface30A of the semiconductor substrate 30 and the lower electrode 11. Aprotective layer 18 is provided on the upper electrode 15. Alight-shielding film 21 is provided in the protective layer 18, forexample, above the readout electrode 11A. It is sufficient if thislight-shielding film 21A is provided to cover the region of the readoutelectrode 11A in direct contact with at least the n-type photoelectricconversion layer 14 without overlapping at least the accumulationelectrode 11B. For example, it is preferable that the light-shieldingfilm 21 be slightly larger than the readout electrode 11A formed in thesame layer as the accumulation electrode 11B. In addition, for example,a color filter 22 is provided, for example, above the accumulationelectrode 11B. The color filter 22 prevents, for example, visible lightfrom being inputted to the n-type photoelectric conversion layer 14, andit is sufficient if the color filter 22 is provided to cover at leastthe region of the accumulation electrode 11B. It is to be noted thatFIG. 1 illustrates an example in which the light-shielding film 21 andthe color filter 22 are provided at different positions in the filmthickness direction of the protective layer 18, but the light-shieldingfilm 21 and the color filter 22 may be provided at the same positions.Optical members such as a flattening layer (not illustrated) and anon-chip lens 23 are disposed above the protective layer 18.

The fixed charge layer 16A may be a film having a positive fixed chargeor a film having a negative fixed charge. Materials of the film having anegative fixed charge include hafnium oxide, aluminum oxide, zirconiumoxide, tantalum oxide, titanium oxide, and the like. In addition, as amaterial other than the above-described materials, lanthanum oxide,praseodymium oxide, cerium oxide, neodymium oxide, promethium oxide,samarium oxide, europium oxide, gadolinium oxide, terbium oxide,dysprosium oxide, holemium oxide, thulium oxide, ytterbium oxide,lutetium oxide, yttrium oxide, an aluminum nitride film, a hafniumoxynitride film, an aluminum oxynitride film, or the like may be used.

The fixed charge layer 16A may also have a configuration in which two ormore types of films are stacked. This makes it possible to furtherimprove a function of a hole accumulation layer in a case of a filmhaving a negative fixed charge, for example.

Materials of the dielectric layer 16B are not limited in particular, butthe dielectric layer 16B includes, for example, a silicon oxide film,TEOS, a silicon nitride film, a silicon oxynitride film, or the like.

The inter-layer insulation layer 17 includes, for example, asingle-layer film including one of silicon oxide, silicon nitride,silicon oxynitride (SiON), and the like, or a stacked film including twoor more thereof.

The protective layer 18 includes a material having light transmissivity,and includes, for example, a single-layer film including any of siliconoxide, silicon nitride, silicon oxynitride, and the like, or a stackedfilm including two or more thereof. The protective layer 18 has athickness of 100 nm to 30000 nm, for example.

The through electrode 34 is provided between the first surface 30A andsecond surface 30B of the semiconductor substrate 30. The photoelectricconversion element 10 is coupled, via this through electrode 34, to agate Gamp of the amplifier transistor AMP and the one source/drainregion 36B of the reset transistor RST (reset transistor Tr1 rst) alsoserving as the floating diffusion FD1. This makes it possible in theimaging element 1 to favorably transfer signal charges generated in thephotoelectric conversion element 10 on the first surface 30A side of thesemiconductor substrate 30 onto the second surface 30B side of thesemiconductor substrate 30 via the through electrode 34, and improvecharacteristics.

The lower end of the through electrode 34 is coupled to the couplingsection 41A in the wiring layer 41, and the coupling section 41A and thegate Gamp of the amplifier transistor AMP are coupled via a lower firstcontact 45. The coupling section 41A and the floating diffusion FD1(region 36B) are coupled via the lower second contact 46, for example.The upper end of the through electrode 34 is coupled to the readoutelectrode 11A via the pad section 39A and the upper first contact 17A,for example.

The through electrode 34 has a function of a connector for thephotoelectric conversion element 10 and the gate Gamp of the amplifiertransistor AMP, and the floating diffusion FD1, and serves as atransmission path for the charges (electrons here) generated in thephotoelectric conversion element 10.

A reset gate Grst of the reset transistor RST is disposed next to thefloating diffusion FD1 (one source/drain region 36B of the resettransistor RST). This makes it possible to cause the reset transistorRST to reset the charges accumulated in the floating diffusion FD1.

The semiconductor substrate 30 includes, for example, an n-type silicon(Si) substrate, and has a p-well 31 in a predetermined region. Thesecond surface 30B of the p-well 31 is provided with the above-describedamplifier transistor AMP, reset transistor RST, selection transistorSEL, and the like. In addition, a peripheral portion of thesemiconductor substrate 30 is provided with a peripheral circuit (notillustrated) including a logic circuit or the like.

The reset transistor RST (reset transistor Tr1 rst) resets the chargestransferred from the photoelectric conversion element 10 to the floatingdiffusion FD1, and includes, for example, an MOS transistor.Specifically, the reset transistor Tr1 rst includes the reset gate Grst,a channel formation region 36A, and source/drain regions 36B and 36C.The reset gate Grst is coupled to a reset line RST1. One source/drainregion 36B of the reset transistor Tr1 rst also serves as the floatingdiffusion FD1. The other source/drain region 36C included in the resettransistor Tr1 rst is coupled to a power supply VDD.

The amplifier transistor AMP is a modulation element that modulates,into a voltage, the amount of charges generated in the photoelectricconversion element 10, and includes, for example, an MOS transistor.Specifically, the amplifier transistor AMP includes the gate Gamp, achannel formation region 35A, and source/drain regions 35B and 35C. Thegate Gamp is coupled to the readout electrode 11A and one source/drainregion 36B (floating diffusion FD1) of the reset transistor Tr1 rst viathe lower first contact 45, the coupling section 41A, the lower secondcontact 46, the through electrode 34, and the like. In addition, the onesource/drain region 35B shares a region with the other source/drainregion 36C included in the reset transistor Tr1 rst, and is coupled tothe power supply VDD.

The selection transistor SEL (selection transistor TR1sel) includes agate Gsel, a channel formation region 34A, and source/drain regions 34Band 34C. The gate Gsel is coupled to a selection line SEL1. In addition,the one source/drain region 34B shares a region with the othersource/drain region 35C included in the amplifier transistor AMP, andthe other source/drain region 34C is coupled to a signal line (dataoutput line) VSL1.

The reset line RST1 and the selection line SEL1 are each coupled to avertical drive circuit 112 included in the drive circuit. The signalline (data output line) VSL1 is coupled to a column signal processingcircuit 113 included in the drive circuit.

The lower first contact 45, the upper first contact 17A, an upper secondcontact 17B, and the upper third contact 17C each include, for example,a doped silicon material such as PDAS (Phosphorus Doped AmorphousSilicon), or a metallic material such as aluminum (Al), tungsten (W),titanium (Ti), cobalt (Co), hafnium (Hf), or tantalum (Ta).

(1-2. Method of Manufacturing Imaging Element)

The imaging element 1 according to the present embodiment ismanufacturable as follows, for example.

FIGS. 6A to 6E each illustrate a method of manufacturing the imagingelement 1 in the order of steps. First, as illustrated in FIG. 6A, forexample, the p-well 31 is formed in the semiconductor substrate 30 as afirst electrically-conductive well. A p+ region is formed near the firstsurface 30A of the semiconductor substrate 30.

As also illustrated in FIG. 6A, an n+ region serving as the floatingdiffusion FD1 is formed on the second surface 30B of the semiconductorsubstrate 30, and a gate insulation layer 32 and a gate wiring layer 47are then formed. The gate wiring layer 47 includes the respective gatesof the selection transistor SEL, amplifier transistor AMP, and resettransistor RST. This forms the selection transistor SEL, the amplifiertransistor AMP, and the reset transistor RST. Further, the multilayerwiring line 40 is formed on the second surface 30B of the semiconductorsubstrate 30. The multilayer wiring line 40 includes the wiring layers41 to 43 and the insulation layer 44. The wiring layers 41 to 43 includethe lower first contact 45, the lower second contact 46, and thecoupling section 41A.

As a base of the semiconductor substrate 30, for example, an SOI(Silicon on Insulator) substrate is used in which the semiconductorsubstrate 30, an embedded oxide film (not illustrated), and a holdingsubstrate (not illustrated) are stacked. The embedded oxide film and theholding substrate are not illustrated in FIG. 6A, but are joined to thefirst surface 30A of the semiconductor substrate 30. After ionimplantation, an annealing process is performed.

Then, a support substrate (not illustrated), another semiconductor base,or the like is joined to the second surface 30B side (multilayer wiringline 40 side) of the semiconductor substrate 30, and flipped vertically.Subsequently, the semiconductor substrate 30 is separated from theembedded oxide film and holding substrate of the SOI substrate to exposethe first surface 30A of the semiconductor substrate 30. It is possibleto perform these steps with technology used in a normal CMOS processsuch as ion implantation and CVD (Chemical Vapor Deposition).

The semiconductor substrate 30 is then processed from the first surface30A side, for example, by dry etching, and an annular opening 34H isformed, for example, as illustrated in FIG. 6B. The depth of the opening34H extends from the first surface 30A to the second surface 30B of thesemiconductor substrate 30 as illustrated in FIG. 6B, and reaches thecoupling section 41A, for example.

Subsequently, for example, the negative fixed charge layer 16A is formedon the first surface 30A of the semiconductor substrate 30 and the sidesurface of the opening 34H. Two or more types of films may be stacked asthe negative fixed charge layer 16A. This makes it possible to furtherimprove the function of the hole accumulation layer. The dielectriclayer 16B is formed after the negative fixed charge layer 16A is formed.Next, the pad sections 39A, 39B, and 39C are formed at predeterminedpositions on the dielectric layer 16B, and the inter-layer insulationlayer 17 is then formed on the dielectric layer 16B and the pad sections39A, 39B, and 39C. Subsequently, the inter-layer insulation layer 17 isformed, and the surface of the inter-layer insulation layer 17 is thenflattened, for example, by using CMP (Chemical Mechanical Polishing).

Subsequently, openings 18H1, 18H2, and 18H3 are formed in theinter-layer insulation layer 17 on the pad sections 39A, 39B, and 39C,respectively, and these openings 18H1, 18H2, and 18H3 are then filled,for example, with electrically-conductive materials such as A1 to forman upper first contact 18A, an upper second contact 18B, and an upperthird contact 18C as illustrated in FIG. 6C.

Subsequently, an electrically-conductive film 21 x is formed on theinter-layer insulation layer 17, and photoresists PR are then formed atpredetermined positions (e.g., on the pad section 39A, the pad section39B, and the pad section 39C) on the electrically-conductive film 21 xas illustrated in FIG. 6D. Thereafter, the readout electrode A, theaccumulation electrode 11B, and the transfer electrode 11C illustratedin FIG. 6E are patterned by etching and removing the photoresists PR.

Subsequently, the insulation layer 12 is then formed above theinter-layer insulation layer 17 and the readout electrode 11A, and theaccumulation electrode 11B and the upper third contact 18C. Thereafter,the opening 12H is provided on the readout electrode 11A. Thereafter,the semiconductor layer 13, the n-type photoelectric conversion layer14, the upper electrode 15, the protective layer 18, the light-shieldingfilm 21, and the color filter 22 are formed above the inter-layerinsulation layer 17. Lastly, the optical members such as the flatteninglayer and the on-chip lens 23 are disposed. As described above, theimaging element 1 illustrated in FIG. 1 is completed.

(1-3. Method of Controlling Imaging Element) (Acquisition of Signal byPhotoelectric Conversion Element 10)

In the imaging element 1 according to the present embodiment, the lightin the near-infrared region in light inputted to the imaging element 1is selectively detected (absorbed) and subjected to photoelectricconversion by the photoelectric conversion element 10.

The photoelectric conversion element 10 is coupled to the gate Gamp ofthe amplifier transistor AMP and the floating diffusion FD1 via thethrough electrode 34. Therefore, the electrons (signal charges) of theelectron-hole pairs generated at the photoelectric conversion element 10are drawn out from the lower electrode 11 side, transferred onto thesecond surface 30B side of the semiconductor substrate 30 via thethrough electrode 34, and accumulated in the floating diffusion FD1. Atthe same time as this, the amplifier transistor AMP modulates the amountof charges generated in the photoelectric conversion element 10 into avoltage.

In addition, the reset gate Grst of the reset transistor RST is disposednext to the floating diffusion FD1. This causes the reset transistor RSTto reset the charges accumulated in the floating diffusion FD1.

In the present embodiment, the photoelectric conversion element 10 iscoupled to not only the amplifier transistor AMP, but also the floatingdiffusion FD1 via the through electrode 34, making it possible tofacilitate the reset transistor RST to reset the charges accumulated inthe floating diffusion FD1.

In contrast, in a case where the through electrode 34 and the floatingdiffusion FD1 are not coupled, it is difficult to reset the chargesaccumulated in the floating diffusion FD1, resulting in application of alarge voltage to pull out the charges to the upper electrode 15 side.The n-type photoelectric conversion layer 14 may be thus damaged. Inaddition, a structure that enables resetting in a short period of timeleads to increased dark-time noise and results in a trade-off. Thisstructure is thus difficult.

FIG. 7 illustrates an operation example of the photoelectric conversionelement 10. (A) indicates a potential at the accumulation electrode 11B,(B) indicates a potential at the floating diffusion FD1 (readoutelectrode 11A), and (C) indicates a potential at the gate (Gsel) of thereset transistor TR1 rst. In the photoelectric conversion element 10,respective voltages are individually applied to the readout electrode11A, the accumulation electrode 11B, and the transfer electrode 11C.

In the photoelectric conversion element 10, a potential V1 is applied tothe readout electrode 11A from the drive circuit, and a potential V2 isapplied to the accumulation electrode 11B in an accumulation period.Here, it is assumed that the potentials V1 and V2 satisfy V1>V2. Thiscauses signal charges (electrons here) generated by photoelectricconversion to be attracted to the accumulation electrode 11B andaccumulated in the region of the semiconductor layer 13 opposed to theaccumulation electrode 11B (accumulation period). Incidentally, thepotential of the region of the semiconductor layer 13 opposed to theaccumulation electrode 11B has a value that is more positive with thepassage of time of photoelectric conversion. It is to be noted thatholes are sent from the upper electrode 15 to the drive circuit.

In the photoelectric conversion element 10, a reset operation isperformed in the latter half of the accumulation period. Specifically,at timing t1, a scanning section changes the voltage of a reset signalRST from a low level to a high level. This turns on the reset transistorTR1 rst in the unit pixel P. As a result, the voltage of the floatingdiffusion FD1 is set at a power supply voltage VDD, and the voltage ofthe floating diffusion FD1 is reset (reset period).

After the reset operation is completed, the charges are read out.Specifically, at timing t2, a potential V3 is applied to the readoutelectrode 11A from the drive circuit, a potential V4 is applied to theaccumulation electrode 11B, and a potential V5 is applied to thetransfer electrode 11C. Here, it is assumed that the potentials V3, V4,and V5 satisfy V4>V5>V3. This causes the signal charges accumulated inthe region corresponding to the accumulation electrode 11B to move fromthe accumulation electrode 11B to the transfer electrode 11C and thereadout electrode 11A in sequence, and be read out from the readoutelectrode 11A to the floating diffusion FD1. That is, the chargesaccumulated in the semiconductor layer 13 are read out to the controlsection (transfer period).

After a readout operation is finished, the potential V1 is applied tothe readout electrode 11A from the drive circuit, and the potential V2is applied to the accumulation electrode 11B again. This causes thesignal charges generated by photoelectric conversion to be attracted tothe accumulation electrode 11B and accumulated in the region of thesemiconductor layer 13 opposed to the accumulation electrode 11B(accumulation period).

(1-4. Workings and Effects)

As described above, a photoelectric conversion element in which asemiconductor nanoparticle is used for a photoelectric conversion layerhas been recently developed as a photoelectric conversion element havinga sensitivity to near-infrared light. The photoelectric conversionelement in which a semiconductor nanoparticle is used for thephotoelectric conversion layer is provided with a semiconductor layerbetween the lower electrode and the photoelectric conversion layer, forexample, like a photoelectric conversion element 1000 illustrated inFIG. 8 from the perspective of reset noise. The semiconductor layeraccumulates the charges generated in the photoelectric conversion layeron a charge accumulating electrode included in the lower electrode, andtransfers the accumulated charges to a charge collecting electrode. Thesemiconductor layer is formed, for example, by using an oxidesemiconductor material such as IGZO, which has a high charge mobility.The photoelectric conversion element in which the semiconductor layerand the photoelectric conversion layer including a semiconductornanoparticle are stacked, however, has concerns about increased darkcurrents and decreased quantum efficiency.

FIG. 8 illustrates potential distribution between electrodes when atypical photoelectric conversion element is irradiated with light. Ahorizontal axis in FIG. 8 indicates a distance from an interface betweenan electrode disposed at a light incidence side and a photoelectricconversion layer. Thus, a film thickness of 0 nm corresponds to aninterface with the electrode disposed at the light incidence side, afilm thickness of 300 nm corresponds to an interface with an electrodedisposed on the other side of the light incidence side, and a filmthickness of 200 nm corresponds to an interface between thephotoelectric conversion layer and the semiconductor layer. Solid linesin FIG. 8 represent potential distribution between electrodes of aphotoelectric conversion element including a semiconductor layer havinga dielectric constant of 10 and an intrinsic photoelectric conversionlayer having a dielectric constant of 30 at a donor density (N_(D)) of10¹⁵ cm⁻³, for example. Dashed lines in FIG. 9 represents potentialdistribution between electrodes of a photoelectric conversion elementincluding a semiconductor layer having a dielectric constant of 10 andan intrinsic photoelectric conversion layer having a dielectric constantof 30 at a donor density (N_(D)) of 10¹⁸ cm⁻³, for example. In thetypical photoelectric conversion element, as illustrated in FIG. 9, itis appreciated that the energy change in the range of 0 nm to 200 nmcorresponding to the photoelectric conversion layer is small compared tothe energy change in the range of 200 nm to 300 nm corresponding to thesemiconductor layer, and an inner electric field applied to thephotoelectric conversion layer when irradiated with light is weak.Further, it is appreciated that the lower the carrier density (donordensity) of the semiconductor layer to be bonded, the harder it is toapply the inner electric field to the photoelectric conversion layerwhen irradiated with light.

It is known that quantum efficiency of photoelectric conversion elementis increased by stacking an n-type semiconductor layer and aphotoelectric conversion layer. In contrast, in a photoelectricconversion element in which a plurality of independent electrodes isprovided on the opposite side to a light incidence side to cause chargesgenerated by photoelectric conversion to be accumulated in thesemiconductor layer, it is necessary that the semiconductor layer bedepleted for accumulation and transfer operation of the charges.Stacking of the depleted semiconductor layer and the photoelectricconversion layer makes it less likely that the inner electric field isapplied to the photoelectric conversion layer as illustrated in FIG. 8due to the difference in the dielectric constants between the depletedsemiconductor layer and the photoelectric conversion layer. Therefore,the transfer of charges comes to depend on diffusion conduction, and thequantum efficiency is reduced.

In contrast, in the photoelectric conversion element (photoelectricconversion element 10) according to the present embodiment, the n-typephotoelectric conversion layer 14 that is n-type doped is provided asthe photoelectric conversion layer. FIG. 9 illustrates potentialdistribution between electrodes when the photoelectric conversionelement 10 is irradiated with light. A horizontal axis in FIG. 9indicates, as in FIG. 8, indicates a distance from an interface betweenthe electrode (upper electrode 15) disposed at the light incidence sideand the photoelectric conversion layer (n-type photoelectric conversionlayer 14). Thus, a film thickness of 0 nm corresponds to an interfacewith the upper electrode 15, a film thickness of 300 corresponds to aninterface with the lower electrode 11, and a film thickness of 200 nmcorresponds to an interface between the n-type photoelectric conversionlayer 14 and the semiconductor layer 13. Solid lines in FIG. 9 representpotential distribution between electrodes of the photoelectricconversion element including the photoelectric conversion layeraccording to the present embodiment. Dashed lines in FIG. 9 representspotential distribution between electrodes of the photoelectricconversion element including the intrinsic photoelectric conversionlayer illustrated in FIG. 8 serving as a comparative example. It is tobe noted that the respective semiconductor layers used in the bothphotoelectric conversion elements each have a donor density (N_(D)) of10¹⁵ cm⁻³. In the photoelectric conversion element 10 according to thepresent embodiment, as illustrated in FIG. 9, it is appreciated that astrong inner electric field is applied to the n-type photoelectricconversion layer 14 when irradiated with light as compared to thecomparative example. Therefore, the efficiency is increased oftransporting electrons generated in the n-type photoelectric conversionlayer 14 to the accumulation electrode 11B, and it becomes possible tosuppress recombination of electron-hole pairs in the n-typephotoelectric conversion layer 14.

As described above, in the present embodiment, the n-type photoelectricconversion layer 14 is stacked as a photoelectric conversion layer onthe semiconductor layer 13 provided on the lower electrode 11 includingthe plurality of electrodes independent from each other; therefore, astrong electric field is applied to the n-type photoelectric conversionlayer 14. This is because as a result of electrons in the n-typephotoelectric conversion layer 14 diffusing into the semiconductor layer13, positive space charges are formed in the n-type photoelectricconversion layer 14 in the vicinity of the bonding surface, and thepotential energy of the n-type photoelectric conversion layer 14 isdepressed. Therefore, the recombination of charges in the n-typephotoelectric conversion layer 14 is suppressed, and it becomes possibleto increase the quantum efficiency.

<2. Application Examples> (Application Example 1)

FIG. 10 illustrates the overall configuration of an imaging device(imaging device 100) including the imaging element 1 described in theabove-described embodiment for each pixel. This imaging device 100 is aCMOS image sensor, and includes a pixel section 1 a as an imaging areaand a peripheral circuit section 130 in a peripheral region of thispixel section 1 a on the semiconductor substrate 30. The peripheralcircuit section 130 includes, for example, a row scanner 131, ahorizontal selector 133, a column scanner 134, and a system controller132.

The pixel section 1 a includes, for example, the plurality of unitpixels P two-dimensionally disposed in a matrix. In these unit pixels P,pixel drive lines Lread (specifically, a row selection line and a resetcontrol line) are disposed in each of pixel rows, for example, andvertical signal lines Lsig are disposed in each of pixel columns. Thepixel drive lines Lread are each used to transmit drive signals forreading out signals from pixels. One end of each of the pixel drivelines Lread is coupled to the output end of the row scanner 131corresponding to each row.

The row scanner 131 is a pixel driver that includes a shift register, anaddress decoder, and the like, and drives each of the unit pixels P ofthe pixel section 1 a on a row basis, for example. A signal outputtedfrom each of the unit pixels P of the pixel rows selectively scanned bythe row scanner 131 is supplied to the horizontal selector 133 througheach of the vertical signal lines Lsig. The horizontal selector 133includes an amplifier, a horizontal selection switch, and the likeprovided for each of the vertical signal lines Lsig.

The column scanner 134 includes a shift register, an address decoder,and the like, and drives each of the horizontal selection switches ofthe horizontal selector 133 in sequence while scanning the horizontalselection switches. The selective scanning by this column scanner 134causes the signals of the respective pixels transmitted through therespective vertical signal lines Lsig to be outputted in sequence to ahorizontal signal line 135, and transmitted to the outside of thesemiconductor substrate 30 through the horizontal signal line 135.

Circuit components including the row scanner 131, the horizontalselector 133, the column scanner 134, and the horizontal signal line 135may be formed directly on the semiconductor substrate 30 or disposed inexternal control IC. In addition, those circuit components may be formedon another substrate coupled by a cable or the like.

The system controller 132 receives a clock supplied from the outside ofthe semiconductor substrate 30, data on instructions of operation modes,and the like, and outputs data such as internal information of theimaging device 100. The system controller 132 further includes a timinggenerator that generates various timing signals, and controls thedriving of the peripheral circuits such as the row scanner 131, thehorizontal selector 133, and the column scanner 134 on the basis of thevarious timing signals generated by the timing generator.

(Application Example 2)

The above-described imaging device 100 or the like is applicable, forexample, to any type of electronic apparatuses each having an imagingfunction such as a camera system including a digital still camera, avideo camera, or the like, and a mobile phone having an imagingfunction. FIG. 11 illustrates the schematic configuration of anelectronic apparatus 200 (camera) as an example thereof. This electronicapparatus 200 is, for example, a video camera that is able to shoot astill image or a moving image. The electronic apparatus 200 includes theimaging device 100, an optical system (optical lens) 210, a shutterdevice 211, a drive section 213 that drives the imaging device 100 andthe shutter device 211, and a signal processing section 212.

The optical system 210 guides image light (incident light) from asubject to the pixel section 1 a of the imaging device 100. This opticalsystem 210 may include a plurality of optical lenses. The shutter device211 controls periods for irradiating the imaging device 100 with lightand shielding the imaging device 100 from light. The drive section 213controls a transfer operation of the imaging device 100 and a shutteroperation of the shutter device 211. The signal processing section 212performs various kinds of signal processing on a signal outputted fromthe imaging device 100. An image signal Dout subjected to the signalprocessing is stored in a storage medium such as a memory or outputtedto a monitor or the like.

(Application Example 3) <Example of Practical Application to In-VivoInformation Acquisition System>

Further, the technology (present technology) according to the presentdisclosure is applicable to various products. For example, thetechnology according to the present disclosure may be applied to anendoscopic surgery system.

FIG. 12 is a block diagram depicting an example of a schematicconfiguration of an in-vivo information acquisition system of a patientusing a capsule type endoscope, to which the technology according to anembodiment of the present disclosure (present technology) can beapplied.

The in-vivo information acquisition system 10001 includes a capsule typeendoscope 10100 and an external controlling apparatus 10200.

The capsule type endoscope 10100 is swallowed by a patient at the timeof inspection. The capsule type endoscope 10100 has an image pickupfunction and a wireless communication function and successively picks upan image of the inside of an organ such as the stomach or an intestine(hereinafter referred to as in-vivo image) at predetermined intervalswhile it moves inside of the organ by peristaltic motion for a period oftime until it is naturally discharged from the patient. Then, thecapsule type endoscope 10100 successively transmits information of thein-vivo image to the external controlling apparatus 10200 outside thebody by wireless transmission.

The external controlling apparatus 10200 integrally controls operationof the in-vivo information acquisition system 10001. Further, theexternal controlling apparatus 10200 receives information of an in-vivoimage transmitted thereto from the capsule type endoscope 10100 andgenerates image data for displaying the in-vivo image on a displayapparatus (not depicted) on the basis of the received information of thein-vivo image.

In the in-vivo information acquisition system 10001, an in-vivo imageimaged a state of the inside of the body of a patient can be acquired atany time in this manner for a period of time until the capsule typeendoscope 10100 is discharged after it is swallowed.

A configuration and functions of the capsule type endoscope 10100 andthe external controlling apparatus 10200 are described in more detailbelow.

The capsule type endoscope 10100 includes a housing 10101 of the capsuletype, in which a light source unit 10111, an image pickup unit 10112, animage processing unit 10113, a wireless communication unit 10114, apower feeding unit 10115, a power supply unit 10116 and a control unit10117 are accommodated.

The light source unit 10111 includes a light source such as, forexample, a light emitting diode (LED) and irradiates light on an imagepickup field-of-view of the image pickup unit 10112.

The image pickup unit 10112 includes an image pickup element and anoptical system including a plurality of lenses provided at a precedingstage to the image pickup element. Reflected light (hereinafter referredto as observation light) of light irradiated on a body tissue which isan observation target is condensed by the optical system and introducedinto the image pickup element. In the image pickup unit 10112, theincident observation light is photoelectrically converted by the imagepickup element, by which an image signal corresponding to theobservation light is generated. The image signal generated by the imagepickup unit 10112 is provided to the image processing unit 10113.

The image processing unit 10113 includes a processor such as a centralprocessing unit (CPU) or a graphics processing unit (GPU) and performsvarious signal processes for an image signal generated by the imagepickup unit 10112. The image processing unit 10113 provides the imagesignal for which the signal processes have been performed thereby as RAWdata to the wireless communication unit 10114.

The wireless communication unit 10114 performs a predetermined processsuch as a modulation process for the image signal for which the signalprocesses have been performed by the image processing unit 10113 andtransmits the resulting image signal to the external controllingapparatus 10200 through an antenna 10114A. Further, the wirelesscommunication unit 10114 receives a control signal relating to drivingcontrol of the capsule type endoscope 10100 from the externalcontrolling apparatus 10200 through the antenna 10114A. The wirelesscommunication unit 10114 provides the control signal received from theexternal controlling apparatus 10200 to the control unit 10117.

The power feeding unit 10115 includes an antenna coil for powerreception, a power regeneration circuit for regenerating electric powerfrom current generated in the antenna coil, a voltage booster circuitand so forth. The power feeding unit 10115 generates electric powerusing the principle of non-contact charging.

The power supply unit 10116 includes a secondary battery and storeselectric power generated by the power feeding unit 10115. In FIG. 12, inorder to avoid complicated illustration, an arrow mark indicative of asupply destination of electric power from the power supply unit 10116and so forth are omitted. However, electric power stored in the powersupply unit 10116 is supplied to and can be used to drive the lightsource unit 10111, the image pickup unit 10112, the image processingunit 10113, the wireless communication unit 10114 and the control unit10117.

The control unit 10117 includes a processor such as a CPU and suitablycontrols driving of the light source unit 10111, the image pickup unit10112, the image processing unit 10113, the wireless communication unit10114 and the power feeding unit 10115 in accordance with a controlsignal transmitted thereto from the external controlling apparatus10200.

The external controlling apparatus 10200 includes a processor such as aCPU or a GPU, a microcomputer, a control board or the like in which aprocessor and a storage element such as a memory are mixedlyincorporated. The external controlling apparatus 10200 transmits acontrol signal to the control unit 10117 of the capsule type endoscope10100 through an antenna 10200A to control operation of the capsule typeendoscope 10100. In the capsule type endoscope 10100, an irradiationcondition of light upon an observation target of the light source unit10111 can be changed, for example, in accordance with a control signalfrom the external controlling apparatus 10200. Further, an image pickupcondition (for example, a frame rate, an exposure value or the like ofthe image pickup unit 10112) can be changed in accordance with a controlsignal from the external controlling apparatus 10200. Further, thesubstance of processing by the image processing unit 10113 or acondition for transmitting an image signal from the wirelesscommunication unit 10114 (for example, a transmission interval, atransmission image number or the like) may be changed in accordance witha control signal from the external controlling apparatus 10200.

Further, the external controlling apparatus 10200 performs various imageprocesses for an image signal transmitted thereto from the capsule typeendoscope 10100 to generate image data for displaying a picked upin-vivo image on the display apparatus. As the image processes, varioussignal processes can be performed such as, for example, a developmentprocess (demosaic process), an image quality improving process(bandwidth enhancement process, a super-resolution process, a noisereduction (NR) process and/or image stabilization process) and/or anenlargement process (electronic zooming process). The externalcontrolling apparatus 10200 controls driving of the display apparatus tocause the display apparatus to display a picked up in-vivo image on thebasis of generated image data. Alternatively, the external controllingapparatus 10200 may also control a recording apparatus (not depicted) torecord generated image data or control a printing apparatus (notdepicted) to output generated image data by printing.

An example of the in-vivo information acquisition system to which thetechnology according to the present disclosure may be applied has beendescribed above. The technology according to the present disclosure maybe applied, for example, to the image pickup unit 10112 among thecomponents described above. This makes it possible to increase thedetection accuracy.

(Application Example 4) <Example of Practical Application to EndoscopicSurgery System>

The technology (present technology) according to the present disclosureis applicable to various products. For example, the technology accordingto the present disclosure may be applied to an endoscopic surgerysystem.

FIG. 13 is a view depicting an example of a schematic configuration ofan endoscopic surgery system to which the technology according to anembodiment of the present disclosure (present technology) can beapplied.

In FIG. 13, a state is illustrated in which a surgeon (medical doctor)11131 is using an endoscopic surgery system 11000 to perform surgery fora patient 11132 on a patient bed 11133. As depicted, the endoscopicsurgery system 11000 includes an endoscope 11100, other surgical tools11110 such as a pneumoperitoneum tube 11111 and an energy device 11112,a supporting arm apparatus 11120 which supports the endoscope 11100thereon, and a cart 11200 on which various apparatus for endoscopicsurgery are mounted.

The endoscope 11100 includes a lens barrel 11101 having a region of apredetermined length from a distal end thereof to be inserted into abody cavity of the patient 11132, and a camera head 11102 connected to aproximal end of the lens barrel 11101. In the example depicted, theendoscope 11100 is depicted which includes as a rigid endoscope havingthe lens barrel 11101 of the hard type. However, the endoscope 11100 mayotherwise be included as a flexible endoscope having the lens barrel11101 of the flexible type.

The lens barrel 11101 has, at a distal end thereof, an opening in whichan objective lens is fitted. A light source apparatus 11203 is connectedto the endoscope 11100 such that light generated by the light sourceapparatus 11203 is introduced to a distal end of the lens barrel 11101by a light guide extending in the inside of the lens barrel 11101 and isirradiated toward an observation target in a body cavity of the patient11132 through the objective lens. It is to be noted that the endoscope11100 may be a forward-viewing endo scope or may be an oblique-viewingendoscope or a side-viewing endoscope.

An optical system and an image pickup element are provided in the insideof the camera head 11102 such that reflected light (observation light)from the observation target is condensed on the image pickup element bythe optical system. The observation light is photo-electricallyconverted by the image pickup element to generate an electric signalcorresponding to the observation light, namely, an image signalcorresponding to an observation image. The image signal is transmittedas RAW data to a CCU 11201.

The CCU 11201 includes a central processing unit (CPU), a graphicsprocessing unit (GPU) or the like and integrally controls operation ofthe endoscope 11100 and a display apparatus 11202. Further, the CCU11201 receives an image signal from the camera head 11102 and performs,for the image signal, various image processes for displaying an imagebased on the image signal such as, for example, a development process(demosaic process).

The display apparatus 11202 displays thereon an image based on an imagesignal, for which the image processes have been performed by the CCU11201, under the control of the CCU 11201.

The light source apparatus 11203 includes a light source such as, forexample, a light emitting diode (LED) and supplies irradiation lightupon imaging of a surgical region to the endoscope 11100.

An inputting apparatus 11204 is an input interface for the endoscopicsurgery system 11000. A user can perform inputting of various kinds ofinformation or instruction inputting to the endoscopic surgery system11000 through the inputting apparatus 11204. For example, the user wouldinput an instruction or a like to change an image pickup condition (typeof irradiation light, magnification, focal distance or the like) by theendoscope 11100.

A treatment tool controlling apparatus 11205 controls driving of theenergy device 11112 for cautery or incision of a tissue, sealing of ablood vessel or the like. A pneumoperitoneum apparatus 11206 feeds gasinto a body cavity of the patient 11132 through the pneumoperitoneumtube 11111 to inflate the body cavity in order to secure the field ofview of the endoscope 11100 and secure the working space for thesurgeon. A recorder 11207 is an apparatus capable of recording variouskinds of information relating to surgery. A printer 11208 is anapparatus capable of printing various kinds of information relating tosurgery in various forms such as a text, an image or a graph.

It is to be noted that the light source apparatus 11203 which suppliesirradiation light when a surgical region is to be imaged to theendoscope 11100 may include a white light source which includes, forexample, an LED, a laser light source or a combination of them. Where awhite light source includes a combination of red, green, and blue (RGB)laser light sources, since the output intensity and the output timingcan be controlled with a high degree of accuracy for each color (eachwavelength), adjustment of the white balance of a picked up image can beperformed by the light source apparatus 11203. Further, in this case, iflaser beams from the respective RGB laser light sources are irradiatedtime-divisionally on an observation target and driving of the imagepickup elements of the camera head 11102 are controlled in synchronismwith the irradiation timings. Then images individually corresponding tothe R, G and B colors can be also picked up time-divisionally. Accordingto this method, a color image can be obtained even if color filters arenot provided for the image pickup element.

Further, the light source apparatus 11203 may be controlled such thatthe intensity of light to be outputted is changed for each predeterminedtime. By controlling driving of the image pickup element of the camerahead 11102 in synchronism with the timing of the change of the intensityof light to acquire images time-divisionally and synthesizing theimages, an image of a high dynamic range free from underexposed blockedup shadows and overexposed highlights can be created.

Further, the light source apparatus 11203 may be configured to supplylight of a predetermined wavelength band ready for special lightobservation. In special light observation, for example, by utilizing thewavelength dependency of absorption of light in a body tissue toirradiate light of a narrow band in comparison with irradiation lightupon ordinary observation (namely, white light), narrow band observation(narrow band imaging) of imaging a predetermined tissue such as a bloodvessel of a superficial portion of the mucous membrane or the like in ahigh contrast is performed. Alternatively, in special light observation,fluorescent observation for obtaining an image from fluorescent lightgenerated by irradiation of excitation light may be performed. Influorescent observation, it is possible to perform observation offluorescent light from a body tissue by irradiating excitation light onthe body tissue (autofluorescence observation) or to obtain afluorescent light image by locally injecting a reagent such asindocyanine green (ICG) into a body tissue and irradiating excitationlight corresponding to a fluorescent light wavelength of the reagentupon the body tissue. The light source apparatus 11203 can be configuredto supply such narrow-band light and/or excitation light suitable forspecial light observation as described above.

FIG. 14 is a block diagram depicting an example of a functionalconfiguration of the camera head 11102 and the CCU 11201 depicted inFIG. 13.

The camera head 11102 includes a lens unit 11401, an image pickup unit11402, a driving unit 11403, a communication unit 11404 and a camerahead controlling unit 11405. The CCU 11201 includes a communication unit11411, an image processing unit 11412 and a control unit 11413. Thecamera head 11102 and the CCU 11201 are connected for communication toeach other by a transmission cable 11400.

The lens unit 11401 is an optical system, provided at a connectinglocation to the lens barrel 11101. Observation light taken in from adistal end of the lens barrel 11101 is guided to the camera head 11102and introduced into the lens unit 11401. The lens unit 11401 includes acombination of a plurality of lenses including a zoom lens and afocusing lens.

The number of image pickup elements which is included by the imagepickup unit 11402 may be one (single-plate type) or a plural number(multi-plate type). Where the image pickup unit 11402 is configured asthat of the multi-plate type, for example, image signals correspondingto respective R, G and B are generated by the image pickup elements, andthe image signals may be synthesized to obtain a color image. The imagepickup unit 11402 may also be configured so as to have a pair of imagepickup elements for acquiring respective image signals for the right eyeand the left eye ready for three dimensional (3D) display. If 3D displayis performed, then the depth of a living body tissue in a surgicalregion can be comprehended more accurately by the surgeon 11131. It isto be noted that, where the image pickup unit 11402 is configured asthat of stereoscopic type, a plurality of systems of lens units 11401are provided corresponding to the individual image pickup elements.

Further, the image pickup unit 11402 may not necessarily be provided onthe camera head 11102. For example, the image pickup unit 11402 may beprovided immediately behind the objective lens in the inside of the lensbarrel 11101.

The driving unit 11403 includes an actuator and moves the zoom lens andthe focusing lens of the lens unit 11401 by a predetermined distancealong an optical axis under the control of the camera head controllingunit 11405. Consequently, the magnification and the focal point of apicked up image by the image pickup unit 11402 can be adjusted suitably.

The communication unit 11404 includes a communication apparatus fortransmitting and receiving various kinds of information to and from theCCU 11201. The communication unit 11404 transmits an image signalacquired from the image pickup unit 11402 as RAW data to the CCU 11201through the transmission cable 11400.

In addition, the communication unit 11404 receives a control signal forcontrolling driving of the camera head 11102 from the CCU 11201 andsupplies the control signal to the camera head controlling unit 11405.The control signal includes information relating to image pickupconditions such as, for example, information that a frame rate of apicked up image is designated, information that an exposure value uponimage picking up is designated and/or information that a magnificationand a focal point of a picked up image are designated.

It is to be noted that the image pickup conditions such as the framerate, exposure value, magnification or focal point may be designated bythe user or may be set automatically by the control unit 11413 of theCCU 11201 on the basis of an acquired image signal. In the latter case,an auto exposure (AE) function, an auto focus (AF) function and an autowhite balance (AWB) function are incorporated in the endoscope 11100.

The camera head controlling unit 11405 controls driving of the camerahead 11102 on the basis of a control signal from the CCU 11201 receivedthrough the communication unit 11404.

The communication unit 11411 includes a communication apparatus fortransmitting and receiving various kinds of information to and from thecamera head 11102. The communication unit 11411 receives an image signaltransmitted thereto from the camera head 11102 through the transmissioncable 11400.

Further, the communication unit 11411 transmits a control signal forcontrolling driving of the camera head 11102 to the camera head 11102.The image signal and the control signal can be transmitted by electricalcommunication, optical communication or the like.

The image processing unit 11412 performs various image processes for animage signal in the form of RAW data transmitted thereto from the camerahead 11102.

The control unit 11413 performs various kinds of control relating toimage picking up of a surgical region or the like by the endoscope 11100and display of a picked up image obtained by image picking up of thesurgical region or the like. For example, the control unit 11413 createsa control signal for controlling driving of the camera head 11102.

Further, the control unit 11413 controls, on the basis of an imagesignal for which image processes have been performed by the imageprocessing unit 11412, the display apparatus 11202 to display a pickedup image in which the surgical region or the like is imaged. Thereupon,the control unit 11413 may recognize various objects in the picked upimage using various image recognition technologies. For example, thecontrol unit 11413 can recognize a surgical tool such as forceps, aparticular living body region, bleeding, mist when the energy device11112 is used and so forth by detecting the shape, color and so forth ofedges of objects included in a picked up image. The control unit 11413may cause, when it controls the display apparatus 11202 to display apicked up image, various kinds of surgery supporting information to bedisplayed in an overlapping manner with an image of the surgical regionusing a result of the recognition. Where surgery supporting informationis displayed in an overlapping manner and presented to the surgeon11131, the burden on the surgeon 11131 can be reduced and the surgeon11131 can proceed with the surgery with certainty.

The transmission cable 11400 which connects the camera head 11102 andthe CCU 11201 to each other is an electric signal cable ready forcommunication of an electric signal, an optical fiber ready for opticalcommunication or a composite cable ready for both of electrical andoptical communications.

Here, while, in the example depicted, communication is performed bywired communication using the transmission cable 11400, thecommunication between the camera head 11102 and the CCU 11201 may beperformed by wireless communication.

An example of the endoscopic surgery system to which the technologyaccording to the present disclosure may be applied has been describedabove. The technology according to the present disclosure may be appliedto the image pickup unit 11402 among the components described above.Applying the technology according to an embodiment of the presentdisclosure to the image pickup unit 11402 increases the detectionaccuracy.

It is to be noted that the endoscopic surgery system has been describedhere as an example, but the technology according to the presentdisclosure may be additionally applied to, for example, a microscopicsurgery system or the like.

(Application Example 5) <Example of Practical Application to MobileBody>

The technology according to the present disclosure is applicable tovarious products. For example, the technology according to the presentdisclosure may be achieved as a device mounted on any type of mobilebody such as a vehicle, an electric vehicle, a hybrid electric vehicle,a motorcycle, a bicycle, a personal mobility, an airplane, a drone, avessel, a robot, a construction machine, or an agricultural machine(tractor).

FIG. 15 is a block diagram depicting an example of schematicconfiguration of a vehicle control system as an example of a mobile bodycontrol system to which the technology according to an embodiment of thepresent disclosure can be applied.

The vehicle control system 12000 includes a plurality of electroniccontrol units connected to each other via a communication network 12001.In the example depicted in FIG. 15, the vehicle control system 12000includes a driving system control unit 12010, a body system control unit12020, an outside-vehicle information detecting unit 12030, anin-vehicle information detecting unit 12040, and an integrated controlunit 12050. In addition, a microcomputer 12051, a sound/image outputsection 12052, and a vehicle-mounted network interface (I/F) 12053 areillustrated as a functional configuration of the integrated control unit12050.

The driving system control unit 12010 controls the operation of devicesrelated to the driving system of the vehicle in accordance with variouskinds of programs. For example, the driving system control unit 12010functions as a control device for a driving force generating device forgenerating the driving force of the vehicle, such as an internalcombustion engine, a driving motor, or the like, a driving forcetransmitting mechanism for transmitting the driving force to wheels, asteering mechanism for adjusting the steering angle of the vehicle, abraking device for generating the braking force of the vehicle, and thelike.

The body system control unit 12020 controls the operation of variouskinds of devices provided to a vehicle body in accordance with variouskinds of programs. For example, the body system control unit 12020functions as a control device for a keyless entry system, a smart keysystem, a power window device, or various kinds of lamps such as aheadlamp, a backup lamp, a brake lamp, a turn signal, a fog lamp, or thelike. In this case, radio waves transmitted from a mobile device as analternative to a key or signals of various kinds of switches can beinput to the body system control unit 12020. The body system controlunit 12020 receives these input radio waves or signals, and controls adoor lock device, the power window device, the lamps, or the like of thevehicle.

The outside-vehicle information detecting unit 12030 detects informationabout the outside of the vehicle including the vehicle control system12000. For example, the outside-vehicle information detecting unit 12030is connected with an imaging section 12031. The outside-vehicleinformation detecting unit 12030 makes the imaging section 12031 imagean image of the outside of the vehicle, and receives the imaged image.On the basis of the received image, the outside-vehicle informationdetecting unit 12030 may perform processing of detecting an object suchas a human, a vehicle, an obstacle, a sign, a character on a roadsurface, or the like, or processing of detecting a distance thereto.

The imaging section 12031 is an optical sensor that receives light, andwhich outputs an electric signal corresponding to a received lightamount of the light. The imaging section 12031 can output the electricsignal as an image, or can output the electric signal as informationabout a measured distance. In addition, the light received by theimaging section 12031 may be visible light, or may be invisible lightsuch as infrared rays or the like.

The in-vehicle information detecting unit 12040 detects informationabout the inside of the vehicle. The in-vehicle information detectingunit 12040 is, for example, connected with a driver state detectingsection 12041 that detects the state of a driver. The driver statedetecting section 12041, for example, includes a camera that images thedriver. On the basis of detection information input from the driverstate detecting section 12041, the in-vehicle information detecting unit12040 may calculate a degree of fatigue of the driver or a degree ofconcentration of the driver, or may determine whether the driver isdozing.

The microcomputer 12051 can calculate a control target value for thedriving force generating device, the steering mechanism, or the brakingdevice on the basis of the information about the inside or outside ofthe vehicle which information is obtained by the outside-vehicleinformation detecting unit 12030 or the in-vehicle information detectingunit 12040, and output a control command to the driving system controlunit 12010. For example, the microcomputer 12051 can perform cooperativecontrol intended to implement functions of an advanced driver assistancesystem (ADAS) which functions include collision avoidance or shockmitigation for the vehicle, following driving based on a followingdistance, vehicle speed maintaining driving, a warning of collision ofthe vehicle, a warning of deviation of the vehicle from a lane, or thelike.

In addition, the microcomputer 12051 can perform cooperative controlintended for automatic driving, which makes the vehicle to travelautonomously without depending on the operation of the driver, or thelike, by controlling the driving force generating device, the steeringmechanism, the braking device, or the like on the basis of theinformation about the outside or inside of the vehicle which informationis obtained by the outside-vehicle information detecting unit 12030 orthe in-vehicle information detecting unit 12040.

In addition, the microcomputer 12051 can output a control command to thebody system control unit 12020 on the basis of the information about theoutside of the vehicle which information is obtained by theoutside-vehicle information detecting unit 12030. For example, themicrocomputer 12051 can perform cooperative control intended to preventa glare by controlling the headlamp so as to change from a high beam toa low beam, for example, in accordance with the position of a precedingvehicle or an oncoming vehicle detected by the outside-vehicleinformation detecting unit 12030.

The sound/image output section 12052 transmits an output signal of atleast one of a sound and an image to an output device capable ofvisually or auditorily notifying information to an occupant of thevehicle or the outside of the vehicle. In the example of FIG. 15, anaudio speaker 12061, a display section 12062, and an instrument panel12063 are illustrated as the output device. The display section 12062may, for example, include at least one of an on-board display and ahead-up display.

FIG. 16 is a diagram depicting an example of the installation positionof the imaging section 12031.

In FIG. 16, the imaging section 12031 includes imaging sections 12101,12102, 12103, 12104, and 12105.

The imaging sections 12101, 12102, 12103, 12104, and 12105 are, forexample, disposed at positions on a front nose, sideview mirrors, a rearbumper, and a back door of the vehicle 12100 as well as a position on anupper portion of a windshield within the interior of the vehicle. Theimaging section 12101 provided to the front nose and the imaging section12105 provided to the upper portion of the windshield within theinterior of the vehicle obtain mainly an image of the front of thevehicle 12100. The imaging sections 12102 and 12103 provided to thesideview mirrors obtain mainly an image of the sides of the vehicle12100. The imaging section 12104 provided to the rear bumper or the backdoor obtains mainly an image of the rear of the vehicle 12100. Theimaging section 12105 provided to the upper portion of the windshieldwithin the interior of the vehicle is used mainly to detect a precedingvehicle, a pedestrian, an obstacle, a signal, a traffic sign, a lane, orthe like.

Incidentally, FIG. 16 depicts an example of photographing ranges of theimaging sections 12101 to 12104. An imaging range 12111 represents theimaging range of the imaging section 12101 provided to the front nose.Imaging ranges 12112 and 12113 respectively represent the imaging rangesof the imaging sections 12102 and 12103 provided to the sideviewmirrors. An imaging range 12114 represents the imaging range of theimaging section 12104 provided to the rear bumper or the back door. Abird's-eye image of the vehicle 12100 as viewed from above is obtainedby superimposing image data imaged by the imaging sections 12101 to12104, for example.

At least one of the imaging sections 12101 to 12104 may have a functionof obtaining distance information. For example, at least one of theimaging sections 12101 to 12104 may be a stereo camera constituted of aplurality of imaging elements, or may be an imaging element havingpixels for phase difference detection.

For example, the microcomputer 12051 can determine a distance to eachthree-dimensional object within the imaging ranges 12111 to 12114 and atemporal change in the distance (relative speed with respect to thevehicle 12100) on the basis of the distance information obtained fromthe imaging sections 12101 to 12104, and thereby extract, as a precedingvehicle, a nearest three-dimensional object in particular that ispresent on a traveling path of the vehicle 12100 and which travels insubstantially the same direction as the vehicle 12100 at a predeterminedspeed (for example, equal to or more than 0 km/hour). Further, themicrocomputer 12051 can set a following distance to be maintained infront of a preceding vehicle in advance, and perform automatic brakecontrol (including following stop control), automatic accelerationcontrol (including following start control), or the like. It is thuspossible to perform cooperative control intended for automatic drivingthat makes the vehicle travel autonomously without depending on theoperation of the driver or the like.

For example, the microcomputer 12051 can classify three-dimensionalobject data on three-dimensional objects into three-dimensional objectdata of a two-wheeled vehicle, a standard-sized vehicle, a large-sizedvehicle, a pedestrian, a utility pole, and other three-dimensionalobjects on the basis of the distance information obtained from theimaging sections 12101 to 12104, extract the classifiedthree-dimensional object data, and use the extracted three-dimensionalobject data for automatic avoidance of an obstacle. For example, themicrocomputer 12051 identifies obstacles around the vehicle 12100 asobstacles that the driver of the vehicle 12100 can recognize visuallyand obstacles that are difficult for the driver of the vehicle 12100 torecognize visually. Then, the microcomputer 12051 determines a collisionrisk indicating a risk of collision with each obstacle. In a situationin which the collision risk is equal to or higher than a set value andthere is thus a possibility of collision, the microcomputer 12051outputs a warning to the driver via the audio speaker 12061 or thedisplay section 12062, and performs forced deceleration or avoidancesteering via the driving system control unit 12010. The microcomputer12051 can thereby assist in driving to avoid collision.

At least one of the imaging sections 12101 to 12104 may be an infraredcamera that detects infrared rays. The microcomputer 12051 can, forexample, recognize a pedestrian by determining whether or not there is apedestrian in imaged images of the imaging sections 12101 to 12104. Suchrecognition of a pedestrian is, for example, performed by a procedure ofextracting characteristic points in the imaged images of the imagingsections 12101 to 12104 as infrared cameras and a procedure ofdetermining whether or not it is the pedestrian by performing patternmatching processing on a series of characteristic points representingthe contour of the object. When the microcomputer 12051 determines thatthere is a pedestrian in the imaged images of the imaging sections 12101to 12104, and thus recognizes the pedestrian, the sound/image outputsection 12052 controls the display section 12062 so that a squarecontour line for emphasis is displayed so as to be superimposed on therecognized pedestrian. The sound/image output section 12052 may alsocontrol the display section 12062 so that an icon or the likerepresenting the pedestrian is displayed at a desired position.

<3. Working Examples>

Next, working examples of the present disclosure are described indetail.

A sample for evaluation was fabricated by using the following method,and the quantum efficiency (QE) and responsiveness were evaluated.

First, a glass substrate having a film thickness of 50 nm provided withan ITO electrode was washed by UV/ozone treatment, and thereafter, asemiconductor layer including IGZO and having a thickness of 100 nm wasformed by sputtering on the ITO electrode. Subsequently, this substratewas subjected to heat treatment for one hour at 350° C., in theatmosphere to deplete the IGZO. Next, ink was applied by spin coatingonto the semiconductor layer as a photoelectric conversion layer at arotation speed of 2500 rpm. The ink was obtained by dispersing PbSnanoparticles in an octane solvent at a concentration of 50 mg/ml. Oleicacid was coordinated to each of the PbS nanoparticles on thenanoparticle surface. Subsequently, a solution was dripped under theatmosphere that was obtained by dispersing TBAI (tetrabutylammoniumiodide) in a methanol solvent at a concentration of 0.1 vol %, immersiontreatment was performed for 10 seconds, and a ligand exchange was madefrom the oleic acid to the TBAI. Next, methanol was dripped to wash offexcess organic substances such as oleic acid. This operation wasrepeated ten times to form a photoelectric conversion layer having athickness of approximately 300 nm. After the layer formation, heattreatment was performed for five minutes at 120° C. in an inactive gasatmosphere to remove a residual solvent. Subsequently, an MoO₃ filmhaving a thickness of 10 nm was formed by vacuum deposition on thephotoelectric conversion layer, and an ITO film of 50 nm was thenstacked by sputtering to form an upper electrode. As described above, aphotoelectric conversion element (sample 1) including a photoelectricconversion region of 1 mm×1 mm was fabricated.

A carrier density and a polarity of the photoelectric conversion layerobtained above were estimated from gate voltage-drain currentcharacteristics and drain voltage-drain current characteristics of athin-film transistor having, as an active layer, a photoelectricconversion layer fabricated separately using a similar method. Thethin-film transistor had a gate electrode using Al on a glass substrate,a gate insulation film in which an Al₂O₃ surface is modified withtrichlorooctadecylsilane, and was fabricated by forming, as the activelayer, the photoelectric conversion layer using a similar method as thephotoelectric conversion element, and Al was used as a source/drainelectrode. The photoelectric conversion layer of sample 1 thus obtainedwas p-type, and the carrier density thereof was p=1×10¹⁶ cm⁻³.

In addition, as samples 2 to 6, photoelectric conversion elements havingn-type photoelectric conversion layers differing in carrier density werefabricated. Specifically, a solution in which TBAI or TBAB(tetrabutylammonium bromide) was dispersed in a methanol solvent at aconcentration of 0.1 vol % to 5 vol % was dripped under an inertatmosphere, and immersion time was adjusted in a range of 10 seconds to200 seconds to thereby fabricate samples each having corresponding oneof the carrier densities of n=3×10¹⁶ cm⁻³ (sample 2), n=1×10¹⁷ cm⁻³(sample 3), n=4×10¹⁷ cm⁻³ (sample 4), n=7×10¹⁷ cm⁻³ (sample 5), andn=1×10¹⁸ cm⁻³ (sample 6). It is to be noted that the method offabricating a sample after the ligand exchange is similar to sample 1.

FIG. 17 is a characteristic diagram summarizing a relationship betweenthe carrier density and the quantum efficiency of the photoelectricconversion layer using samples 1 to 6 described above. It is to be notedthat the vertical axis of FIG. 17 indicates a relative value in whichthe quantum efficiency of sample 1 having the p-type photoelectricconversion layer is set to 1. From FIG. 17, it was confirmed that in thephotoelectric conversion element including the semiconductornanoparticle, the quantum efficiency was increased by providing then-type photoelectric conversion layer on the semiconductor layer.Further, it was appreciated that the carrier density of the n-typephotoelectric conversion layer is preferably set to n=3×10¹⁶ cm⁻³ ormore and 1×10¹⁸ cm⁻³ or less, and more preferably set to 1×10¹⁷ cm⁻³ ormore and 7×10¹⁷ cm⁻³ or less. It is noted that the decrease in thequantum efficiency when doping concentration was set to 7×10¹⁷ cm⁻³ ormore is considered to be due to that the n-type photoelectric conversionlayer in the vicinity of the bonding surface between the n-typephotoelectric conversion layer and the semiconductor layer is stronglydepleted by positive fixed charges, thereby causing the electron densityin the photoelectric conversion layer to be excessive, weakening theinner electric field of the photoelectric conversion layer, andpromoting the recombination of charges.

The above has given description with reference to the embodiment, theapplication examples, and the working examples, but the content of thepresent disclosure is not limited to the above-described embodiment andthe like, and various modifications are possible. For example, in theabove-described embodiment, the example has been described in which thephotoelectric conversion element 10 is used alone in the imaging element1. The photoelectric conversion element 10 performs photoelectricconversion on the light having the wavelength of the near-infraredregion. However, for example, another photoelectric conversion elementmay be combined and used that performs photoelectric conversion on lightsuch as visible light having the wavelength of a region other than thenear-infrared region. Examples of the other photoelectric conversionelement include a so-called inorganic photoelectric conversion elementembedded and formed in the semiconductor substrate 30, and a so-calledorganic photoelectric conversion element in which a photoelectricconversion layer is formed by using an organic semiconductor material.

In addition, in the above-described embodiment and the like, theconfiguration of the back-illuminated imaging element 1 is described asan example. However, it is also possible to apply the embodiment and thelike to a front-illuminated imaging element. Further, in a case whereanother photoelectric conversion element is combined and used asdescribed above, the imaging element 1 may be configured as a so-calledvertical spectral type imaging element or may be an imaging elementincluding a semiconductor substrate on which photoelectric conversionelements that perform photoelectric conversion on the light withinanother wavelength range are two-dimensionally arranged (e.g., Bayerarrangement). Furthermore, for example, a substrate provided withanother functional device such as a memory element may be stacked on themultilayer wiring side.

In addition, the photoelectric conversion element 10, and imagingelement 1 and imaging device 100 according to the present disclosureeach do not necessarily have to include all of the respective componentsdescribed in the above-described embodiment and the like, but mayinclude another layer on the contrary.

Furthermore, it is possible to apply the technology according to thedisclosure to a photovoltaic cell, for example, in addition to theimaging device.

It is to be noted that the effects described herein are merely examples,but not limitative. In addition, there may be other effects.

It is to be noted that the present disclosure may have the followingconfigurations.

(1) A photoelectric conversion element including:

-   -   a first electrode including a plurality of electrodes        independent from each other;    -   a second electrode disposed to be opposed to the first        electrode;    -   an n-type photoelectric conversion layer including a        semiconductor nanoparticle, the n-type photoelectric conversion        layer being provided between the first electrode and the second        electrode; and    -   a semiconductor layer including an oxide semiconductor material,        the semiconductor layer being provided between the first        electrode and the n-type photoelectric conversion layer.

(2) The photoelectric conversion element according to (1), in which then-type photoelectric conversion layer has a carrier density of 3×10¹⁶cm⁻³ or more and 1×10¹⁸ cm⁻³ or less.

(3) The photoelectric conversion element according to (1) or (2), inwhich the semiconductor layer has a carrier density of 1×10¹⁷ cm⁻³ orless.

(4) The photoelectric conversion element according to any one of (1) to(3), in which

-   -   the semiconductor nanoparticle includes a core and a ligand, the        ligand being bound to a surface of the core, and    -   the core includes at least one of PbS, PbSe, PbTe, CuInSe₂,        ZnCuInSe, CuInS₂, HgTe, InAs, InSb, Ag₂S, or CuZnSnSSe.

(5) The photoelectric conversion element according to any one of (1) to(4), in which

-   -   the semiconductor nanoparticle includes a core and a ligand, the        ligand being bound to a surface of the core, and    -   the ligand includes any of a chlorine atom, a bromine atom, and        an iodine atom.

(6) The photoelectric conversion element according to (4) or (5), inwhich

-   -   the semiconductor nanoparticle further includes a shell provided        around the core, and    -   the shell includes at least one of PbO, PbO₂, Pb₃O₄, ZnS, ZnSe,        and ZnTe.

(7) The photoelectric conversion element according to any one of (1) to(6), in which the semiconductor layer includes at least one of IGZO,ZTO, Zn₂SnO₄, InGaZnSnO, GTO, Ga₂O₃:SnO₂, or IGO.

(8) The photoelectric conversion element according to any one of (1) to(7), in which

-   -   the first electrode is formed by using any of titanium (Ti),        silver (Ag), aluminum (Al), magnesium (Mg), chromium (Cr),        nickel (Ni), tungsten (W), and copper (Cu), and    -   the second electrode is formed by using indium tin oxide (ITO).

(9) The photoelectric conversion element according to any one of (1) to(8), including

-   -   an insulation layer between the first electrode and the        semiconductor layer, in which    -   the first electrode includes a charge readout electrode and a        charge accumulation electrode, the charge readout electrode        being electrically coupled to the n-type photoelectric        conversion layer via an opening provided to the insulation        layer, the charge accumulation electrode being disposed to be        opposed to the n-type photoelectric conversion layer with the        insulation layer interposed therebetween.

(10) The photoelectric conversion element according to (9), in which thefirst electrode includes a charge transfer electrode between the chargereadout electrode and the charge accumulation electrode.

(11) The photoelectric conversion element according to any one of (1) to(10), in which respective voltages are individually applied to theplurality of electrodes included in the first electrode.

(12) The photoelectric conversion element according to any one of (1) to(11), further including

-   -   a semiconductor substrate, in which    -   the first electrode, the semiconductor layer, the n-type        photoelectric conversion layer, and the second electrode are        provided in this order on a first surface side of the        semiconductor substrate.

(13) The photoelectric conversion element according to (12), in whichthe semiconductor substrate includes a drive circuit, and the pluralityof electrodes included in the first electrode is each coupled to thedrive circuit.

(14) The photoelectric conversion element according to (12) or (13), inwhich a multilayer wiring layer is formed on a second surface sideopposed to the first surface of the semiconductor substrate.

(15) An imaging device including

-   -   a plurality of pixels each provided with one or more        photoelectric conversion elements,    -   the one or more photoelectric conversion elements each including        -   a first electrode including a plurality of electrodes            independent from each other,        -   a second electrode disposed to be opposed to the first            electrode,        -   an n-type photoelectric conversion layer including a            semiconductor nanoparticle, the n-type photoelectric            conversion layer being provided between the first electrode            and the second electrode, and        -   a semiconductor layer including an oxide semiconductor            material, the semiconductor layer being provided between the            first electrode and the n-type photoelectric conversion            layer.

This application claims the benefit of Japanese Priority PatentApplication JP2018-015406 filed with the Japan Patent Office on Jan. 31,2018, the entire contents of which are incorporated herein by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations, and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A photoelectric conversion element comprising: a first electrodeincluding a plurality of electrodes independent from each other; asecond electrode disposed to be opposed to the first electrode; ann-type photoelectric conversion layer including a semiconductornanoparticle, the n-type photoelectric conversion layer being providedbetween the first electrode and the second electrode; and asemiconductor layer including an oxide semiconductor material, thesemiconductor layer being provided between the first electrode and then-type photoelectric conversion layer.
 2. The photoelectric conversionelement according to claim 1, wherein the n-type photoelectricconversion layer has a carrier density of 3×10¹⁶ cm⁻³ or more and 1×10¹⁸cm⁻³ or less.
 3. The photoelectric conversion element according to claim1, wherein the semiconductor layer has a carrier density of 1×10¹⁷ cm⁻³or less.
 4. The photoelectric conversion element according to claim 1,wherein the semiconductor nanoparticle includes a core and a ligand, theligand being bound to a surface of the core, and the core includes atleast one of PbS, PbSe, PbTe, CuInSe₂, ZnCuInSe, CuInS₂, HgTe, InAs,InSb, Ag₂S, or CuZnSnSSe.
 5. The photoelectric conversion elementaccording to claim 1, wherein the semiconductor nanoparticle includes acore and a ligand, the ligand being bound to a surface of the core, andthe ligand includes any of a chlorine atom, a bromine atom, and aniodine atom.
 6. The photoelectric conversion element according to claim4, wherein the semiconductor nanoparticle further includes a shellprovided around the core, and the shell includes at least one of PbO,PbO₂, Pb₃O₄, ZnS, ZnSe, and ZnTe.
 7. The photoelectric conversionelement according to claim 1, wherein the semiconductor layer includesat least one of IGZO, ZTO, Zn₂SnO₄, InGaZnSnO, GTO, Ga₂O₃:SnO₂, or IGO.8. The photoelectric conversion element according to claim 1, whereinthe first electrode is formed by using any of titanium (Ti), silver(Ag), aluminum (Al), magnesium (Mg), chromium (Cr), nickel (Ni),tungsten (W), and copper (Cu), and the second electrode is formed byusing indium tin oxide (ITO).
 9. The photoelectric conversion elementaccording to claim 1, comprising an insulation layer between the firstelectrode and the semiconductor layer, wherein the first electrodeincludes a charge readout electrode and a charge accumulation electrode,the charge readout electrode being electrically coupled to the n-typephotoelectric conversion layer via an opening provided to the insulationlayer, the charge accumulation electrode being disposed to be opposed tothe n-type photoelectric conversion layer with the insulation layerinterposed therebetween.
 10. The photoelectric conversion elementaccording to claim 9, wherein the first electrode includes a chargetransfer electrode between the charge readout electrode and the chargeaccumulation electrode.
 11. The photoelectric conversion elementaccording to claim 1, wherein respective voltages are individuallyapplied to the plurality of electrodes included in the first electrode.12. The photoelectric conversion element according to claim 1, furthercomprising a semiconductor substrate, wherein the first electrode, thesemiconductor layer, the n-type photoelectric conversion layer, and thesecond electrode are provided in this order on a first surface side ofthe semiconductor substrate.
 13. The photoelectric conversion elementaccording to claim 12, wherein the semiconductor substrate includes adrive circuit, and the plurality of electrodes included in the firstelectrode is each coupled to the drive circuit.
 14. The photoelectricconversion element according to claim 12, wherein a multilayer wiringlayer is formed on a second surface side opposed to the first surface ofthe semiconductor substrate.
 15. An imaging device comprising aplurality of pixels each provided with one or more photoelectricconversion elements, the one or more photoelectric conversion elementseach including a first electrode including a plurality of electrodesindependent from each other, a second electrode disposed to be opposedto the first electrode, an n-type photoelectric conversion layerincluding a semiconductor nanoparticle, the n-type photoelectricconversion layer being provided between the first electrode and thesecond electrode, and a semiconductor layer including an oxidesemiconductor material, the semiconductor layer being provided betweenthe first electrode and the n-type photoelectric conversion layer.